In the prior art, different production methods are known. Among these the one which is most used relates to the rolling of billets from a continuous casting plant. The method progressively thins them in section, until reaching the diameter of the bar, iron rod or wire that must be obtained.
In the case of small rolled sections, it is clear that the work is remarkably expensive, both in terms of time, complexity and cost. In order to be productive, the rolling speed was constantly and continuously increased, greatly exceeding 30 m/sec. for straight bars and 100 m/sec. for bars (wire) to be wound on a bobbin. The speed increase involves limits not easily surmountable, and therefore when the maximum limit is almost reached, it is no longer possible to obtain an appreciable increase if not at prohibitive costs of the plant, production and maintenance.
Attempts have been proposed for parallel rolling, starting from continuous casting in a billet. Parallel rolling has never been successful, and notwithstanding the numerous projects and patents in the prior art, it has never found a large application due to its complexity. The need for intervention on a single line, for example due to jamming, makes rolling on the other line practically impossible.
At present "split" rolling is greatly used, which consists of producing two iron rods from a previous shaping by splitting a stock into two rods, rotating them 90.degree., and further rolling them in a final section (JP-A-60-130401). It is also possible to make four iron rods with two successive splits simultaneously on the same rolling stand, starting from the same billet.
This rolling always starts from a billet coming from a heating furnace, not directly connected to the continuous casting, because the casting speed for billets of sizes conveniently productive (ex. 160.times.160 mm) is very slow, about 3 m/sec. max., equal to an hourly production of 37 Ton/h (theoretically), i.e., low. Such rolling speed (3 m/min-0.05 m/sec.) is not supported by the rolling stands and would cause cracks and failures to the rolls because of excessive heating of the latter. Additionally, starting from a 160.times.160 mm billet to obtain an iron rod of 8.5 mm of diameter, approximately 18 stands are necessary.
To be productive, these plants must have an entrance speed of the billet in the first rolling stand higher than the casting speed (about three times). Consequently, the rolling stands must be fed by more than one continuous casting line (at least 2 or 3 lines).
Another disadvantage is the increase in waste as a result of head and tail discard necessary for each wire produced.
DE-4009861A (SMS) discloses a steel rolling plant for producing "long bars" starting directly from a continuous casting plant (1) with multi-exit casting lines (six lines, ref. 3). The six exit casting lines 3 that are conveyed in a heating furnace and then are orthogonally rolled:
in one solution with a single line of a rolling mill, PA1 in an alternative solution with a plurality of rolling mill lines. PA1 a direct and advantageous productive connection of the rolling mill to the continuous casting, because the casting speed of the thin flat bloom is compatible with the speed of the first rolling stand; PA1 an increase in the production with an advancement speed that is not necessarily high; PA1 a simplification of the plant and a reduction of the space occupied, with obvious reductions also in the infrastructure costs and invested capital; PA1 a reduction of the energy utilized and of energy waste; PA1 a reduction of the maintenance costs due to the simplification of the plant; PA1 a reduction of the use of cooling; PA1 a reduction in personnel also equal production; and PA1 higher control assurance.
This solution has the same inconveniences as the above described solutions.
Patent Abstract of Japan, vol. 7, n.44 (M-195), Feb. 22, 1993 & JP 57193205 disclose a rolling mill plant for rolling a large slab, shaping it in a continuous form to realize a plurality of square sections diagonally disposed and connected in a thin line by their opposite corners. This is obtained along its longitudinal direction by caliber rolling and forming these to steel bars by rolling in succession. The abstract clarifies that the prescribed slab is obtained from steel making, then through ingot making, blooming and continuous casting. This slab is subjected to primary rolling down to a prescribed intermediate thickness, whereby an intermediate blank material is obtained.
This intermediate blank material is heated and is formed with grooves in its longitudinal direction with caliber roughing rolls, after which it is split and cut to plural pieces of square materials with final rolls. These square materials are subjected to secondary rolling and finish rolling in succession, whereby products such as steel bars and steel rolls of the required size are obtained. This solution is a normal solution of transforming a material by a plurality of stages. In this way one is not able to solve the above problems.
Nevertheless, combining the teaching of the last two solutions, we are able to realize a new process or plant able to solve the above problems.